Conductivity improving combination of cerium oxide and detergents for diesel fuels

ABSTRACT

The disclosure provides conductivity improving concentrates and methods for improving conductivity and reducing risks associated with static discharge in middle distillate fuel composition compositions, particularly diesel fuels. The conductivity improvement is provided with the combination of cerium oxide nanoparticles and dispersant/detergent and shows aged conductivity comparable to or higher than that obtained with conventional antistatic agents.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/533,200 filed on Sep. 19, 2006 and entitled Diesel Fuel AdditivesContaining Cerium or Manganese and Detergents.

FIELD OF THE DISCLOSURE

The disclosure relates to diesel fuel additives to impart improvedcombustion, and improved fuel stability to the finished diesel fuel. Thedisclosure also relates to compositions and methods for improving theconductivity of middle distillate fuel compositions, particularly dieselfuels and most particularly low sulfur and ultra-low sulfur dieselfuels.

BACKGROUND OF THE DISCLOSURE

Cerium oxide nanoparticles have been used in diesel fuel applications asa catalyst for converters in the elimination of toxic exhaust emissiongases. Cerium oxide has also shown utility in reducing the emission fromdiesel engines of particulate emissions. Envirox™ Fuel Borne Catalyst isa diesel fuel combustion improver which reduces fuel consumption andalso reduces harmful exhaust emissions.

Certain organometallic compounds have been found effective as combustionimprovers for distillate fuels such as home heating oils and the like.For example, U.S. Pat. No. 3,112,789 describes the use ofcyclopentadienyl manganese tricarbonyls for this purpose, and thecompound methylcyclopentadienyl manganese tricarbonyl (MMT) has beensold in the form of a solution in a hydrocarbon diluent as a combustionimprover for distillate fuels of this type. Bis(cyclopentadienyl) ironhas also been promoted and sold as a combustion improver for use in suchfuels.

U.S. Pat. Nos. 3,883,320 and 3,891,401 teach the addition of salts of atransition metal, such as manganese, and an alkaline earth metal, suchas calcium, to jet fuels for reducing deposits and smoke. These patentsrequire a manganese/calcium weight ratio of about 5/1 and the combinedamounts of metals within the range of from 200 to 600 ppm (200 to 500ppm in the '401 patent).

However, difficulties can arise in the formulating of diesel fuels withcertain additive packages resulting in haze, precipitates,insolubilities, inadequate fuel economy, and insufficient smokereduction. A need has arisen for a fuel-soluble additive composition forhydrocarbonaceous fuels that is not only capable of reducing the amountof soot, smoke and/or carbonaceous products produced on combustion ofthe fuel but that is capable of improving solubility in the fuel, andenhancing fuel economy resulting from the combustion of the fuel. Infulfilling this need, it is also important to provide an additive whichprevents or at least inhibits the deposition of sludge on criticalengine or burner parts or surfaces and which provides fuel compositionshaving satisfactory physical properties such as thermal stability andstorage stability. It is also highly desirable to provide an additivecomposition which is capable of reducing or inhibiting the amount ofnoxious emissions (e.g., carbon monoxide, unburned hydrocarbons,polyaromatic hydrocarbons, and/or particulates) formed when using thefuels in an engine or in a burner or like combustion apparatus. Theprovision of additive compositions capable of decreasing fuelconsumption is also a most desirable objective. A need therefore existsfor an improved diesel fuel additive and diesel fuel additive packagethat provides improved combustion, improved solubility of theorganometallic fuel additives, reduced haze, improved smoke reduction,and enhanced fuel economy.

Certain middle distillate fuel compositions, particularly diesel fuels,are capable of generating static electricity, particularly when movingrapidly, such as when the fuel is being dispensed into a tanker or otherbulk container or vessel. While diesel fuels are not very volatile, thetankers used to transport diesel fuels are also used to transportgasoline, kerosene and other more volatile and flammable liquids. Evenafter the more volatile fuel is dispensed from the tanker, the vaporsmay still be present and pose a risk of fire or explosion from a sparkgenerated by the discharge of static electricity from the fuelcomposition.

These risks have become more acute in recent years with the increasedpopularity and use of low sulfur fuels and even more acute in recentmonths with the introduction of ultra-low sulfur diesel fuels. Theprocess used to remove the sulfur from the fuels also decreases theconcentration of other polar compounds in the fuel, which in turnreduces the ability of the fuel to dissipate a static charge.

To mitigate the risks of fire or explosion with low and ultra-low sulfurfuels, it has become common to add a conductivity improver to the fuelat or prior to the point of dispensing the fuel into a bulk container.The conductivity improver, as the name suggests, improves theconductivity of the fuel, thus permitting any static charge built upduring high volume transport of the fuel to safely dissipate withoutgenerating a spark. Conductivity improvers are also known as antistaticagents.

The most common type of conductivity improver or antistatic agent usedin fuels, particularly diesel fuels, has been the Stadis® brand ofantistatic agents sold by Innospec Fuel Specialties, LLC, Newark, Del.However, the Stadis® brand of antistatic agents contains sulfur. Addingthe Stadis® antistatic agents to the diesel fuel thus reduces certain ofthe benefits of using an ultra-low sulfur fuel. In addition, theseantistatic agents are quite expensive.

Moreover, sulfur-containing antistatic agents present another problemwhen used with additive concentrates or fuels that contain basicnitrogen. Specifically, Applicants have observed that the conductivityimprovement delivered by the traditional antistatic agent dissipatesvery rapidly when used in additive concentrates or fuel mixturescontaining basic nitrogen. This is disadvantageous because it preventspre-blending of these antistatic agents into additive concentrates thatcontain basic nitrogen. Many components of a typically fuel additiveconcentrate include nitrogen-containing compounds, such as dispersants,detergents, cetane number improvers and the like. As a result, it isoften necessary to add the sulfur-containing antistatic agentsseparately from the other components of the additive concentrate. Thus,these types of antistatic agents must be kept in a separate tank at thedepot and added separately to the fuel. Accordingly, these types ofantistatic agent, apart from their inherent additional cost, requireadditional costs and complexity in terms of storage, handling anddispensing.

Therefore, there is a need for compositions and methods to address thebuild-up and discharge of static electricity in middle distillate fuelcompositions.

SUMMARY OF THE EMBODIMENTS

An embodiment presented herein provides a diesel fuel additive packagecontaining a source of cerium, such as cerium oxide particles ornanoparticles, and a diesel fuel detergent.

In one embodiment, the diesel fuel additive package contains ceriumoxide nanoparticles, a cetane number-improving agent, diesel fueldetergent and a demulsifier. More particularly, another embodiment cancontain cerium oxide particles or nanoparticles, a diesel fueldetergent/dispersant containing an alkylated (HR-PIB) succinimidepolyamine and cetane number improver (eg. 2-ethyl hexyl nitrate), ademulsifier and may also contain a metal de-activator.

In one embodiment, the additive package containing cerium oxideparticles or nanoparticles can be used to treat diesel fuel at a treatrate of from about 1 to about 200 ppm in the diesel fuel. Higher andlower levels of cerium oxide will be desirable for certain applications.

The diesel fuel additive package of the present disclosure can alsocontain mixed metal combustion improvers, such as cerium/manganese andcerium/manganese/iron compounds, alloys or mixtures. One embodimentherein employs alloys of two or more metals as, or comprising,nanoparticles for improved solubility or dispersibility in the fuel.

Another embodiment herein provides a diesel fuel containing the ceriumoxide nanoparticles, cetane improver and a detergent, and alow-phosphorus demulsifier.

In another embodiment herein is presented a method of improving theefficiency of a diesel fuel for an internal combustion engine whichcomprises adding to the fuel prior to the introduction of the fuel to avehicle or other apparatus comprising an internal combustion engine adiesel fuel additive package comprising cerium oxide nanoparticles, adetergent and a demulsifier.

Other embodiments herein include methods for improving the efficiency ofa diesel fuel (fuel economy), a method for improving diesel fuelstability, a method for reducing smoke from combustion in a dieselengine, a method for improving the solubility of an organometallic fueladditive in a diesel fuel, a method for reducing the haze in a dieselfuel having diesel fuel additives, a method for foam reduction in adiesel fuel, and a method for reducing filter blockage in a diesel fuelfilter.

In other embodiment, the disclosure provides an additive concentrate fora middle distillate fuel, said concentrate comprising an antistaticagent which antistatic agent comprises, in combination, cerium oxideparticles and a dispersant/detergent and a fuel containing thecombination of cerium oxide particles and a dispersant/detergent as anantistatic agent.

In yet other embodiments, the disclosure provides a method of dispensinga middle distillate fuel comprising the steps of adding to the fuel anantistatic agent comprising, in combination, cerium oxide particles anda dispersant/detergent.

In another embodiment, the disclosure provides a method of reducing therisk of ignition or explosion from static discharge, comprising thesteps of providing a middle distillate fuel, adding adispersant/detergent in combination with cerium oxide particles toimprove the conductivity of the fuel and thus reduce the risk of staticdischarge.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide further explanation of the presentdisclosure, as claimed.

DETAILED DESCRIPTION OF EMBODIMENTS

The present disclosure provides in one embodiment a diesel fuel additivepackage comprising cerium oxide particles or nanoparticles that aresoluble or dispersible in diesel fuel. More importantly, the diesel fueladditive package contains in one embodiment a demulsifier compound toreduce or eliminate the foaming and/or emulsion problems often observedin the pumping, distribution, tank-filling and use of additized dieselfuels.

In one embodiment, the demulsifier employed in the present diesel fueladditive has a phosphorus level of greater than 30 mg/kg of demulsifier.However, it has been presently discovered that by reducing thephosphorus content, whether deliberately present or present as acontaminant, of the demulsifier in the diesel fuel additive, thestability of the fuel additive composition and of the resulting fuel isgreatly enhanced and a significant reduction in haze is obtained. Thus,a level of phosphorus in the demulsifier of up to about 30 mg/kg can beused, or a phosphorus level of about 24 mg/kg has been employed, inanother example about 8 mg/kg of phosphorus was employed, and in yetanother formulation about 0.12 mg/kg phosphorus level was employed inthe diesel fuel demulsifier. As the phosphorus level was reduced, asurprising and unexpected improvement in haze reduction and fuelstability was attained.

Demulsifiers (or dehazers) herein can be any of the commerciallyavailable materials such as but not limited to alkoxylated phenolformaldehyde polymers, such as those commercially available as “NALCO”(Trade Mark) 7007 (ex Nalco), and “TOLAD” (Trade Mark) 2683 (exPetrolite), alkylated phenols and resins derived therefrom, oxylatedalkylphenolic resin, and formaldehyde polymer with4-(1,1-dimethylethyl)phenol, methyloxirane and oxirane, ethoxylatedEO/PO resin, polyglycol ester, ethylene oxide resin.

Therefore, there is presented herein a diesel fuel additive packagecontaining cerium oxide nanoparticles generally having a size notexceeding one micron and in one embodiment not exceeding 300 nm, forexample 1 to 300 nm, such as from 1 to 150 nm, in particular 1 to 50 nm,and especially 1 to 20 nm. This diesel fuel additive package can alsocontain at least one diesel fuel detergent/dispersant selected from thegroup consisting of succinimides, Mannich bases, amides, amines, andpolyetheramines.

In addition, the diesel fuel additive package can contain a demulsifierwith reduced phosphorus levels of, for example, up to about 24 mg/kg, orabout 8 mg/kg to about 24 mg/kg, or from about 0.1 mg/kg to about 8mg/kg. In this manner is achieved a diesel fuel additive package able toimpart to the diesel fuel superior haze reduction, improved additivesolubility, increased fuel stability, smoke reduction, combustionimprovement, and enhanced fuel economy.

Another benefit of the present disclosure is the improvement in theperformance of the demulsifier in its intended performance in the fueladditive and in the finished fuel. Emulsions tend to form in fuelshaving detergents/dispersants, hence the need for the demulsifier. Anyreaction which deactivates or reacts with the demulsifier reduces thedemulsification efficacy, leading to more emulsification. In this manneris provided a method to improve the demulsification of a fuel additivecomprising adding to the fuel additive the cerium oxide nanoparticles, adetergent and a demulsifier, wherein the demulsifier has less than about30 mg/kg phosphorus. In another embodiment, the demulsifier has up toabout 24 mg/kg, or in a separate example about 8 mg/kg to about 24mg/kg, or in yet another example from about 0.1 mg/kg to about 8 mg/kgof phosphorus.

The amounts of cerium oxide nanoparticles, detergent and demulsifieruseful in the embodiments presently disclosed can vary depending on thedesired application, the nature of the diesel fuel, and other desiredcomponents in the additive package or the finished fuel.

In another embodiment is provided a diesel fuel composition thatcomprises a major amount of a diesel fuel and a minor combustionimproving amount of an additive composition comprising: a) one or morefuel-soluble component comprising one or more manganese and/or ceriumcompounds, mixtures or alloys; b) one or more fuel-soluble alkali oralkaline earth metal-containing detergents—e.g., one or more neutral orbasic alkali or alkaline earth metal salts of at least one sulphonicacid, and/or at least one carboxylic acid, and/or at least one salicylicacid, and/or at least one alkylphenol, and/or at least one sulphurisedalkylphenol; and c) a demulsifier of reduced phosphorus content asdefined hereinabove, wherein component a) is present in an amountsufficient to supply from 0.1 to 5 ppm manganese or cerium or both tothe fuel and component b) is present in an amount sufficient to supplyfrom 5 to 50 ppm alkali and/or alkaline earth metal to the fuelcomposition. This embodiment can also contain one or more alkyl nitratecetane number-improving agents.

By improving the conductivity of the fuel, the fuel is better able todissipate a static charge that might be generated by high volumetransportation of the fuel, such as when the fuel is dispensed into atanker truck or rail car. Because the fuel is better able to dissipate astatic charge, the fuel is less likely to generate a spark, which mayignite volatile fumes that might be present in the area, either from thefuel itself or from previous fuels that may have been transported in thetanker.

Certain of the present embodiments are based on the discovery byApplicants that the combination of cerium oxide nanoparticles and adispersant/detergent provide an unexpected and surprising synergisticantistatic benefit to a middle distillate fuel. The embodiments alsoprovide conductivity benefits without adding sulfur-containing compoundslike the Stadis® antistatic agents to an ultra-low sulfur fuel, and thusprovide an environmental benefit as well.

The embodiments are particularly suited for middle distillate fuelcompositions. Middle distillate fuel compositions include, but are notlimited to, jet fuels, diesel fuels, and kerosene. In an embodiment, thefuel is a low-sulfur fuel having less than about 50 ppm sulfur. In anembodiment, the fuel is an ultra-low sulfur diesel fuel or ultra-lowsulfur kerosene. Ultra-low sulfur fuels are generally considered to haveno more than about 15 ppm of sulfur, more preferably no more than 10 ppmof sulfur. The term “diesel fuel” is generally considered to be ageneric term encompassing diesel, biodiesel, biodiesel-derived fuel,synthetic diesel and mixtures thereof. Although biodiesel is nottechnically a distillate fuel, it is nevertheless included within thedefinition of “middle distillate fuel compositions” as that term is usedthroughout this application and in the claims.

The present disclosure encompasses jet fuels, although these areconventionally not regarded as “low-sulfur” or “ultra-low sulfur” fuelssince their sulfur levels can be comparatively quite high. Nevertheless,jet fuels may also benefit from the conductivity improvement of theembodiments regardless of their sulfur content.

The terms “combustion system” and “apparatus” used in the disclosureconnote any apparatus, machine or motor that utilize, in whole or inpart, a combustible fuel to generate power. The terms include, forexample, diesel-electric hybrid vehicle, a gasoline-electric hybridvehicle, a two-stroke engine, any and all burners or combustion units,including for example, stationary burners, waste incinerators, dieselfuel burners, diesel fuel engines, automotive diesel engines, gasolinefuel burners, gasoline fuel engines, power plant generators, and thelike. The hydrocarbonaceous fuel combustion systems that may benefitfrom the present disclosure include all combustion units, systems,devices, and/or engines that burn fuels. The term “combustion system”also encompasses internal and external combustion devices, machines,engines, turbine engines, jet engines, boilers, incinerators,evaporative burners, plasma burner systems, plasma arc, stationaryburners, and the like which can combust or in which can be combusted ahydrocarbonaceous fuel.

Cerium oxide nanoparticles have been used in diesel fuel applications asa catalyst for converters in the elimination of toxic exhaust emissiongases. Cerium oxide has also shown utility in reducing the particulateemission from diesel engines. Envirox™ Fuel Borne Catalyst from Oxonica,Ltd. (Oxfordshire, England), for example, is a diesel fuel combustionimprover which reduces fuel consumption and also reduces harmful exhaustemissions. Cerium oxide particles have also shown benefit of reducinghaze and foam formation in diesel fuels.

Although it is possible to use ordinary cerium oxide particles it hasbeen found to be beneficial in certain of the present embodiments to usecerium oxide which has been doped with components that result inadditional oxygen vacancies being formed. This generally means that thedopant will be di- or tri-valent in order to provide oxygen vacancies.Such dopant ions must be di- or tri-valent ions of an element which is arare earth metal, a transition metal or a metal of Group IIA, IIIB, VB,or VIB of the Periodic Table in order to provide oxygen vacancies. Theymust also be of a size that allows incorporation of the ion within thesurface region of the cerium oxide nanoparticles. Accordingly metalswith a large ionic radius should not be used.

Typically the doped oxides will have the formula Ce_(1−x)M_(x)O₂ where Mis a said metal or metalloid, in particular Rh, Cu, Ag, Au, Pd, Pt, Sb,Se, Fe, Ga, Mg, Mn, Cr, Be, B, Co, V, Zr, Ti and Ca as well as Pr, Smand Gd and x has a value up to 0.3, typically 0.01 or 0.1 to 0.2, or ofthe formula [(CeO₂)_(1−n)(REO_(y))_(n)]_(1−k)M′_(k) where M′ is a saidmetal or metalloid other than a rare earth, RE is a rare earth, y is 1or 1.5 and each of n and k, which may be the same or different, has avalue op to 0.5, preferably up to 0.3, typically 0.01 or 0.1 to 0.2.Further details can be found in our PCT/GB2002/005013 to which referenceshould be made.

In general the cerium oxide particles will have a size not exceeding 1micron and in particular embodiments will not exceed 300 nm in size, forexample 1 to 300 nm, such as from 1 to 150 nm, in particular 1 to 50 nm,especially 1 to 20 nm.

In certain embodiments, it is preferred that the cerium oxide particlesare coated to prevent agglomeration. For this purpose the particles canbe comminuted in an organic solvent in the presence of a coating agentwhich is an organic acid, anhydride or ester or a Lewis base. It hasbeen found that, in this way which involves coating in situ, it ispossible to significantly improve the coating of the oxide. Further, theresulting product can, in many instances, be used directly without anyintermediate step. Thus in some coating procedures it is necessary todry the coated particles before dispersing them in a hydrocarbonsolvent. Thus the cerium oxide particles can be dispersible or solublein the fuel or another hydrocarbon compatible with the fuel.

The particles which are subjected to the process should have as large asurface area as possible and preferably the particles have a surfacearea, before coating, of at least 10 m·sup·2/g and preferably a surfacearea of at least 50 or 75 m²/g, for example 80-150 m²/g, or 100-300m²/g.

The coating process involves comminuting the particles so as to preventany agglomerates from forming. Techniques which can be used for thispurpose include high-speed stirring or tumbling and the use of a colloidmill, ultrasonics or ball milling. Ball milling is preferred. Furtherdetails of such coatings can be found in PCT/GB02/02312.

Typically the concentration of cerium oxide in the additive will be from0.1 to 10%, generally 0.5 to 5%, by weight. Furthermore, the ceriumoxide nanoparticles generally having a size not exceeding one micron andin one embodiment not exceeding 300 nm, for example 1 to 300 nm, such asfrom 1 to 150 nm, in particular 1 to 50 nm, and especially 1 to 20 nm.

It has been found that the cerium oxide particles can be stabilized inthe fuel or fuel additive package by the presence of adetergent/dispersant. As noted, a synergistic antistatic effect is seenwhen the cerium oxide particles and/or doped cerium oxide particles arecombined with a dispersant/detergent. Particular detergents which can beused in the present invention include a basic nitrogen-containingdetergent. Suitable ashless detergents/dispersants include amides,amines, polyetheramines, Mannich bases and succinimides which arepreferred, although metal-containing detergents are also effectiveherein.

These dispersants are described in numerous patent specifications,mainly as additives for use in lubricant compositions, but their use inhydrocarbon fuels has also been described. Ashless dispersants leavelittle or no metal-containing residue on combustion. They generallycontain only carbon, hydrogen, oxygen and in most cases nitrogen, butsometimes contain in addition other non-metallic elements such asphosphorus, sulfur or boron. A particularly useful ashlessdispersant/detergent herein is derived from “high reactive”polyisobutylene (HR-PIB) substituted on a maleic anhydride reacted witha polyamine to achieve a level of about 5.4% nitrogen to achieveenhanced dispersancy. Such a material is available from Afton ChemicalCorporation as HiTEC® 4007. The detergent/dispersant can be used in thefuel additive packages herein at levels of from about 5 to about 20% byweight.

In one embodiment, the detergent is a succinimide, which has an averageof at least 3 nitrogen atoms per molecule. The succinimide is preferablyaliphatic and may be saturated or unsaturated, especially ethylenicallyunsaturated, e.g. an alkyl or alkenyl succinimide. Typically thedetergent is formed from an alkyl or alkenyl succinic acylating agent,generally having at least 35 carbon atoms in the alkyl or alkenyl group,and an alkylene polyamine mixture having an average of at least 3nitrogen atoms per molecule. In another embodiment the polyamine has 4to 6 nitrogen atoms per molecule. Preferably it can be formed from apolyisobutenyl succinic acylating agent derived from polyisobutenehaving a number average molecular weight of 500 to 10,000 and anethylene polyamine which can include cyclic and acyclic parts, having anaverage composition from triethylene tetramine to pentaethylenehexamine. Thus the chain will typically have a molecular weight from 500to 2500, especially 750 to 1500 with those having molecular weightsaround 900 and 1300 being particularly useful although a succinimidewith an aliphatic chain with a molecular weight of about 2100 is alsouseful. Further details can be found in U.S. Pat. Nos. 5,932,525 and6,048,373 and EP-A 432,941, 460309 and 1,237,373.

Examples of suitable metal-containing detergents useful herein include,but are not limited to, such substances as lithium phenates, sodiumphenates, potassium phenates, calcium phenates, magnesium phenates,sulphurised lithium phenates, sulphurised sodium phenates, sulphurisedpotassium phenates, sulphurised calcium phenates, and sulphurisedmagnesium phenates wherein each aromatic group has one or more aliphaticgroups to impart hydrocarbon solubility; the basic salts of any of theforegoing phenols or sulphurised phenols (often referred to as“overbased” phenates or “overbased sulphurised phenates”); lithiumsulfonates, sodium sulfonates, potassium sulfonates, calcium sulfonates,and magnesium sulfonates wherein each sulphonic acid moiety is attachedto an aromatic nucleus which in turn usually contains one or morealiphatic substituents to impart hydrocarbon solubility; the basic saltsof any of the foregoing sulfonates (often referred to as “overbasedsulfonates”; lithium salicylates, sodium salicylates, potassiumsalicylates, calcium salicylates, and magnesium salicylates wherein thearomatic moiety is usually substituted by one or more aliphaticsubstituents to impart hydrocarbon solubility; the basic salts of any ofthe foregoing salicylates (often referred to as “overbasedsalicylates”); the lithium, sodium, potassium, calcium and magnesiumsalts of hydrolysed phosphosulphurised olefins having 10 to 2000 carbonatoms or of hydrolysed phosphosulphurised alcohols and/oraliphatic-substituted phenolic compounds having 10 to 2000 carbon atoms;lithium, sodium, potassium, calcium and magnesium salts of aliphaticcarboxylic acids and aliphatic-substituted cycloaliphatic carboxylicacids; the basic salts of the foregoing carboxylic acids (often referredto as “overbased carboxylates” and many other similar alkali andalkaline earth metal salts of oil-soluble organic acids.

Mixtures of salts of two or more different alkali and/or alkaline earthmetals can be used. Likewise, salts of mixtures of two or more differentacids or two or more different types of acids (e.g., one or more calciumphenates with one or more calcium sulfonates) can also be used. Whilerubidium, cesium and strontium salts are feasible, their expense rendersthem impractical for most uses.

According to one embodiment of the present disclosure, the cerium oxidenanoparticles are added to diesel fuel at an early stage by beingincorporated into the diesel fuel additive package. It has been foundthat incorporating the particles in this way can lead to improved fuelefficiency in the diesel engine by preventing agglomeration and henceloss of surface area of the cerium particles. The present disclosureimproves the previous performance of cerium oxide particles ornanoparticles in fuel by allowing the cerium oxide to more fully performits roles. This is achieved by reducing the cerium removal from the fuelby sediment formation thereby keeping more of the cerium atoms availablefor combustion catalysis and emission reduction or other benefits.

Another benefit of the present disclosure is reduced filter blockage offuel filters because of the reduction in or elimination of sediment,precipitation and/or haze caused by, for example, interactions betweenthe cerium atoms or particles and fuel additive components and/orcontaminants. Malfunctioning fuel filters can lead to difficulties inengine operation and finally to a complete shut down. One example is thereduced interaction between phosphorus and the cerium oxide particles ornanoparticles according to the present disclosure to reduce fuel filterblockage. A measure of this benefit is observable from IP 387 FiltrationTest. Thus, there is provided herein a method to reduce filter blockageof fuel filters in a vehicle or other apparatus employing a dieselengine combusting a diesel fuel and having a fuel filter, said methodcomprising adding to the diesel fuel prior to the introduction of thefuel to a vehicle or other apparatus a diesel fuel additive packagecomprising cerium oxide nanoparticles, a detergent and a demulsifier.

Accordingly, the present disclosure provides a method of improving theefficiency of a fuel for an internal combustion engine which comprisesadding to the fuel prior to the introduction of the fuel to a vehicle orother apparatus comprising an internal combustion engine a fuel solublemetallic material containing cerium oxide and/or a manganese source, anda detergent and a demulsifier as fuel additives. By introducing thecerium oxide in this way there is little or no need for any vehicle fuelmanagement system necessary by other methods of introduction such ason-board dosing. Fuel efficiency will result from the incorporation ofthe cerium oxide particles in the fuel.

Accordingly, the present disclosure also provides a fuel additivecomposition, which comprises cerium oxide nanoparticles and/or amanganese source together with a detergent, preferably an aliphaticsuccinimide and a demulsifier having less than about 8 mg/kg ofphosphorus. In another embodiment the fuel additive composition furthercomprises a demulsifier, as defined hereinabove, and a cetane improveragent.

Typically the concentration of cerium oxide particles or nanoparticlesin the diesel fuel additive will be from 0.1 to 10%, generally 0.5 to5%, by weight.

Typically the fuel additives which are incorporated at a refinery mayinclude cetane number improvers, cold flow improvers, antioxidants, andmetal deactivators. Accordingly the fuel additive compositions of thepresent disclosure can incorporate one or more of these. Thus, thepresent disclosure provides fuel additive compositions comprising ceriumoxide nanoparticles and/or colloids, a detergent, a demulsifier, andoptionally one of more of the components selected from the groupconsisting of cetane number improvers (also called ignitionimprovers)(such as alkyl nitrates), cold flow improvers (such aspolyesters), and antioxidants (such as phenolics eg.2,6-di-tert-butylphenol, or phenylenediamines such asN,N′-di-sec-butyl-p-phenylenediamine), and metal deactivators such assalicylic acid derivatives, e.g. N,N-disalicylidene-1,2-propane diamine.

Lubricity additive, anti-rust agents and antifoamants are also useful inthe diesel fuel additive packages of the present disclosure.

In another embodiment of the present disclosure, the fuel additivecomposition can contain a mixture, blend, compound of or alloy of two ormore metals, plus a detergent/dispersant and a demulsifier with up toabout 30 mg/kg of phosphorus. Mixed metal catalyst systems are known butthe use thereof with detergents and a demulsifier able to reduce oreliminate haze, instability or precipitates is needed and presentlyprovided.

Thus, an improved fuel additive composition of the present disclosurecan comprise a material containing two or more metal-containingcombustion catalysts, a detergent/dispersant, and a demulsifier havingup to about 30 mg/kg of phosphorus. In another embodiment, thedemulsifier has up to about 24 mg/kg, or in a separate example about 8mg/kg to about 24 mg/kg, or in yet another example from about 0.1 mg/kgto about 8 mg/kg of phosphorus. The detergent/dispersant and thedemulsifier can be, for example, as described hereinabove. Thesemetal-containing combustion catalysts can be cerium oxide particles ornanoparticles, manganese sources, such as methylcyclopentadienylmanganese tricarbonyl, and iron sources, such as solubilized iron oxideand ferrocene.

By “manganese” herein is meant any manganese or manganese-containingmaterial, compound or precursor, such as but not limited to methylcyclopentadienyl manganese tricarbonyl, available from Afton ChemicalCorporation as MMT®, and manganese sulfonate, manganese phenate,manganese salicylate, cyclopentadienyl manganese tricarbonyl, alkylcyclopentadienyl manganese tricarbonyl, organic manganese tricarbonylderivatives, alkyl cyclopentadienyl manganese derivatives,bis-cyclopentadienyl manganese, bis-alkyl cyclopentandienyl manganese,neutral and overbased manganese salicylates, neutral and overbasedmanganese phenates, neutral and overbased manganese sulfonates,manganese carboxylates, manganese oxide and combinations and mixturesthereof.

Therefore, a cerium/manganese mixture or alloy can be used herein; acerium/manganese/iron mixture or alloy can be used herein; a cerium/ironmixture or alloy can be used herein; or a manganese/iron mixture oralloy can be used herein.

There is provided herein a fuel additive which comprises cerium oxideand a manganese source, a detergent, and a demulsifier with phosphoruscontent of up to about 24 mg/kg. In a separate example, the phosphorusin the demulsifier is about 8 mg/kg to about 24 mg/kg, or in yet anotherexample from about 0.1 mg/kg to about 8 mg/kg of phosphorus.

Furthermore, cerium oxide particles or nanoparticles can be combinedwith ferrocene (an iron source) in the preparation of a fuel additivecomposition further comprising a detergent/dispersant and a demulsifier.Thus, for example, a fuel additive composition is provided comprisingcerium oxide (e.g. Envirox™ from Oxonica), ferrocene (widely available),a succinimide detergent/dispersant (HiTEC® 4007 from Afton ChemicalCorporation and derived from 950 MW polyisobutylene with greater than70% vinylidene groups plus maleic anhydride, reacted with a polyamine toachieve a final N content of about 6.0%), and a demulsifier (Tolad 9357from Baker Petrolite) which will have excellent combustion improveractivity, no haze or precipitate, good smoke reduction, and enhancedfuel economy.

The compositions and methods of certain of the present embodiments arecapable of providing a conductivity to a fuel of at least 25 pS/m at thetime and temperature of delivery. This conductivity is sufficient tomeet the proposed new ASTM standard for conductivity in diesel fuels(ASTM D975 and amendments and appendices thereto) measured according toany appropriate test procedure, including but not limited to ASTM D2622and ASTM D4951. The conductivity is obtained by the addition of thecerium oxide particles and the detergent alone, thus obviating the needto add conventional antistatic agents such as the Stadis® compounds. Theconductivity benefit provided by the embodiments has been shown to besustained for at least 7 days after the detergent and cerium oxideparticles are combined together. An additional benefit of the presentembodiments is that an antistatic effect is obtained without addingunnecessary sulfur to the fuel composition. For example, the combinationof cerium oxide particles and detergent/dispersant can contribute nomore than about 0.135 ppm of sulfur to the fuel composition, thuspreserving the benefits of using ultra-low sulfur fuels.

EXAMPLES

Model Mixed Metal Systems

The following examples further illustrate aspects of the presentdisclosure but do not limit the present disclosure.

Example 1

Cerium oxide (e.g. Envirox ™ from Oxonica) 1-200 ppm Ferrocene (widelyavailable) 5-30 weight % Detergent/dispersant (HiTEC ® 4007 AftonChemical) 5-15 weight % Demulsifier (Tolad ® 9357 from Baker Petrolite)1-10 weight % Aromatic and/or aliphatic solvent(s) 45-89 weight %

HiTEC® 4656 Diesel Fuel Additive (Afton Chemical Corporation) is basedon about 50% by weight of 2-ethyl hexyl nitrate cetane improver and 15%by weight of a HR-PIB succinimide detergent/dispersant with about 6.0weight % nitrogen (HiTEC® 4007 available from Afton ChemicalCorporation). HiTEC® 4656 was combined with 250 ppm of a source ofcerium oxide particles in aliphatic solvent to deliver 5 ppm of ceriumoxide particles (Envirox™ available from Oxonica). This combination canbe used directly in a diesel fuel or diluted in aliphatic or aromaticsolvent to prepare a diesel fuel additive.

Example 2

Cerium/manganese alloy 1-200 ppm Ferrocene (widely available) 5-30weight % Detergent/dispersant (HiTEC ® 4007 Afton Chemical) 5-15 weight% Demulsifier (Tolad ® 9357 from Baker Petrolite) 1-10 weight % Aromaticand/or aliphatic solvent(s) 45-89 weight %

To improve the fuel stability of the product of Example 1, it wascombined with 2.27% weight percent demulsifier (Tolad® 9338, a blend oflong chain polyglycols, oxyalkylated phenol-formaldehyde resins andoxyalkylated adducts of glycol/epoxide polymers in aliphatic alcoholsand an aromatic hydrocarbon solvent, available from Baker Petrolite).Tolad® 9338 had a phosphorus content of 23.95 mg/kg. However, there wasa high degree of haze, which would be an unacceptable product forvirtually all applications, depending on the shelf life needed and/orthe type of diesel fuel involved. When filtered, sediment of 1.39 gramsper 1 kg was obtained.

Example 3

Cerium/manganese/iron alloy 1-200 ppm Detergent/dispersant (HiTEC ® 4007Afton Chemical) 5-15 weight % Demulsifier (Tolad ® 9357 from BakerPetrolite) 1-10 weight % Aromatic and/or aliphatic solvent(s) 45-89weight %

To improve the solubility and fuel stability the product of Example 1was combined with 2.27% by weight percent of a demulsifier (Tolad® 2898,an oxylated alkylphenolic resin with lower phosphorus content of 7.85mg/kg). The fuel stability was improved and the haze reduced (see below)relative to the results for Example 2, but were not idealized for allfuels or all fuel applications. When filtered, sediment of 0.35 gramsper 1 kg of additive product was obtained.

Example 4

The product of Example 1 was combined with 2.27% by weight percent ofanother demulsifier (Tolad® 9357, formaldehyde polymer with4-(1,1-dimethylethyl)phenol, methyloxirane and oxirane in an aromaticsolvent) which had a phosphorus content of 0.199 mg/kg. This fueladditive package had excellent clarity, very low haze, and noappreciable precipitate (only 0.15 grams of sediment per 1 kg of fueladditive package). This resulting diesel fuel additive package wascombined with diesel fuel at a treat rate of 1350 ppm resulting inexcellent fuel stability, no precipitate and no haze. In this finaldiesel fuel product the cerium oxide content was 0.37 weight % (5 ppm),and the phosphorus level is therefore only a trace amount. The finaldiesel fuel product was considered excellent in terms of smokereduction, fuel economy, fuel stability, solubility and improvedcombustion.

As can be seen from the above examples, when HiTEC® 4656 Diesel FuelAdditive (alkyl nitrate cetane number improver) with Tolad® 9338demulsifier was mixed with Enivrox™ cerium oxide nanoparticles theresulting fuel additive product produced a sediment of 1.39 grams per 1kg of additive. When HiTEC® 4656 Diesel Fuel Additive (alkyl nitratecetane number improver) with Tolad® 2898 demulsifier was mixed withEnivrox™ cerium oxide nanoparticles the product produced a sediment of0.35 grams per 1 kg of additive. When HiTEC® 4656 Diesel Fuel Additive(alkyl nitrate cetane number improver) with Tolad 9357 demulsifier wasmixed with Enivrox™ the product produced a sediment of 0.15 grams per 1kg of additive.

Haze Measurements

Haze Additive Demulse Envirox (NTU) n/a n/a Y 335 H4656 T9338 N 5.74H4656 T2898 N 5.61 H4656 T9357 N 5.18 H4656 T9338 Y 1552 H4656 T2898 Y880 H4656 T9357 Y 175

Clearly the unexpected improvement is the reduction in haze whencombining the cetane number improver, the cerium oxide nanoparticles,and a low phosphorus-containing demulsifier. “NTU” is a unit of measureknown in the industry as “non-arbitrary units.”

Defoaming Experiments

In addition, applicants carried out antifoam testing on the fueladditive products produced containing the alkyl nitrate cetane numberimprover and the cerium oxide nanoparticles with surprising results. Itwas observed that the cerium oxide has a positive influence on foamreduction. With the Envirox™ product alone, the fuel foam decay time washalved, but when used in conjunction with a HiTEC® 4656 type product,the foam performance was improved beyond the normal HiTEC® 4656 foamperformance. Thus, an unexpected benefit is obtained in diesel fuel foamreduction when combining cerium oxide nanoparticles and an alkylnitratecetane number improver.

Day 0 Treat Decay Foam Rate Envirox Time Height Fuel Additive (ppm)(ppm) (sacs) (mols) RF93-T-95 n/a n/a n/a 45 100 RF93-T-95 n/a n/a 25021.2 100 RF93-T-95 H4656 1100 n/a 6.9 80 RF93-T-95 H4656 1100 250 2.8 55

Base reference diesel fuel has a decay time of 45 seconds, with a foamheight of 100 mls. Diesel fuel treated with 250 ppm Envirox™ has a decaytime of 21.2 seconds and a foam height of 100 mls; diesel fuel treatedwith 1100 ppm HiTEC® 4656 has a decay time of 6.9 seconds and a foamheight of 80 mls; and diesel treated with 250 ppm Envirox™ plus 1100 ppmHiTEC® 4656 has a decay time of 2.8 seconds and a foam height of 55 mls.Clearly, there is an unexpected excellent improvement in foam reductionachieved by combining the cerium oxide nanoparticles and the alkylnitrate cetane number improver in the diesel fuel. Thus, there isprovided herein a method for foam reduction in a diesel fuel byproviding to the fuel a fuel additive package comprising cerium oxidenanoparticles and an alkyl nitrate cetane number improver additive.

By the incorporation of the present disclosure into vehicles or devices,significant improvements in mechanical design and methods of use areprovided. In one embodiment herein is provided an emissions controlsystem for the after-treatment of a diesel fuel combustion processexhaust stream comprising: an exhaust passageway for the passage of anexhaust stream containing exhaust byproducts from the combustion of adiesel fuel, a particulate filter selected from the group consisting ofcontinuously regenerating technology diesel particulate filter, a dieselparticulate filter, and a catalyzed diesel particulate filter, locatedwithin the exhaust passageway and adapted to contact the exhaust stream,wherein the fuel has an additive package introduced into it, theadditive package comprising cerium oxide and/or manganese, a detergent,an alkyl nitrate ignition improver, and optionally a demulsifier,whereby the operation of the particulate filter is enhanced bymaximizing the dispersancy of the cerium oxide. This prevents theagglomeration of the cerium oxide particles which would otherwise reducethe interaction of cerium oxide with the exhaust particulates.Furthermore, improved dispersing of the cerium oxide particles accordingto the present disclosure reduces their agglomeration and minimizes oreliminates the potential for fuel filter plugging. In addition, a methodof use is provided for improving the performance of a diesel particulatefilter by reducing the negative impact on the surface of the filterpresent in the absence of the use of the fuel additive packagesdescribed herein.

In certain engine designs, the injector nozzle holes are non-cylindricalbut are flared outwardly with increasing diameter toward the combustionchamber with the intent to keep the injector hole dry after eachinjection of fuel. These designs are found to be extremely prone tocoking which negatively impacts fuel flow, uniformity of combustion, andpromotes deposit build-up because the fuel dynamic flow cannot sweep thesurfaces of the injector holes clean. Therefore a need exists to protectthe injector nozzle hole by improved exposure to the combustion chambergases which will now include the cerium atoms and cerium oxideparticles. By the present disclosure, the cerium and cerium oxideparticles can serve to oxidize and remove the carbonaceous deposits inand around the nozzle hole. Thus is provided herein a method for use ina diesel engine having non-cylindrical injector nozzle holes of a dieselfuel additive package comprising cerium oxide, a detergent/dispersant,and a demulsifier having less than 24 mg/kg pf phosphorus. In a separateexample, the phosphorus in the demulsifier is about 8 mg/kg to about 24mg/kg, or in yet another example from about 0.1 mg/kg to about 8 mg/kgof phosphorus.

Conductivity Examples

Control 1

A sample of RF93-T-95 diesel fuel, which is a reference fuel containing50-500 ppm of sulfur, was measured for conductivity according to IP 274(ASTM D2624). The fuel was then subjected to an aging test in either acold environment (@21° C.) or a hot environment (@50° C.). Two coldsamples were used. After 7 days, the conductivity was again measured.The conductivity of the hot sample was measured directly out of theoven. One cold sample was allowed to sit at room temperature for 1 hourprior to measuring the conductivity, while the other cold sample wasmerely shaken after removing it from the refrigeration unit.

Control 2

Control 1 was repeated, except that 250 ppm (volume) of cerium oxidenanoparticles (Envirox™, average particle size=12 nm) were also added tothe diesel fuel.

Example C1

Control 1 was repeated, except that 1100 ppm (volume) of a fuel additiveconcentrate HiTEC® 4656 (Afton Chemical) was added to the diesel fuel.

Example C2

The procedure for Example 1 was repeated, except that 250 ppm (volume)of cerium oxide nanoparticles (Envirox™, average particle size=12 nm)was also added to the diesel fuel before the additive concentrate wasadded.

Example C3

The procedure for Example 1 was repeated except that, instead of thefuel additive concentrate, 5 ppm (volume) of a traditional antistaticagent (Tolad® 3514 from Baker Petrolite) was added to the diesel fuel.

Example C4

The procedure for Example 3 was repeated except that 250 ppm (volume) ofcerium oxide particles (as in Example 2) was also added to the dieselfuel.

Example C5

The procedure for Example 3 was repeated except that, instead of T3514,5 ppm (volume) of another traditional antistatic agent (Stadis® 450 fromInnospec Fuel Specialties) was added to the diesel fuel.

Example C6

The procedure for Example 5 was repeated except that 250 ppm (volume) ofcerium oxide particles (as in Examples 2 and 4) was also added to thediesel fuel.

Controls 3-4

Controls 1-2 were repeated, except that an ultra-low sulfur diesel fuelcontaining 30 ppm of sulfur was used in place of the RF93-T-95 dieselfuel.

Examples C7-C12

Examples 1-6 were repeated using the ultra-low sulfur diesel fuel fromControls 3-4.

Results from the conductivity examples are reported in Table 1.

TABLE 1 Treat Day 0 Day 7 Day 7 Day 7 Antistatic Rate CeriumConductivity Conductivity Conductivity Conductivity Example Agent (ppmv)oxide (pS) (pS) (pS) (pS) Control 1 N 153 214 160 154 Control 2 Y 188290 201 192 C1 N 796 721 690 725 C2 Y 1197 690 550 523 C3 Tolad ® 3514 5N 788 1438 1059 980 C4 Tolad ® 3514 5 Y 789 1232 992 816 C5 Stadis ® 4505 N 421 772 541 479 C6 Stadis ® 450 5 Y 413 791 520 466 Control 3 N 109176 128 131 Control 4 Y 132 174 135 151 C7 N 552 1070 735 700 C8 Y 8841084 741 694 C9 Tolad ® 3514 5 N 245 323 281 256 C10 Tolad ® 3514 5 Y281 340 282 268 C11 Stadis ® 450 5 N 405 560 431 379 C12 Stadis ® 450 5Y 434 610 461 380

The data demonstrate a synergistic effect that the cerium oxide anddetergent combination have on conductivity in diesel fuels. Moreover,the cerium oxide particles and detergent combination show higher initialconductivity and comparable or better aged conductivity as compared totraditional antistatic agents. Thus, the embodiments provide aconductivity benefit to a diesel fuel without the need to add specialantistatic agents.

Other embodiments of the present disclosure will be apparent to thoseskilled in the art from consideration of the specification and practiceof the disclosure disclosed herein. As used throughout the specificationand claims, “a” and/or “an” may refer to one or more than one. Unlessotherwise indicated, all numbers expressing quantities of ingredients,properties such as molecular weight, percent, ratio, reactionconditions, and so forth used in the specification and claims are to beunderstood as being modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth in the specification and claims are approximations that mayvary depending upon the desired properties sought to be obtained by thepresent disclosure. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of theclaims, each numerical parameter should at least be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques. Notwithstanding that the numerical ranges andparameters setting forth the broad scope of the disclosure areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in their respective testing measurements. It isintended that the specification and examples be considered as exemplaryonly, with a true scope and spirit of the disclosure being indicated bythe following claims.

1. An additive concentrate for a middle distillate fuel composition,said additive concentrate comprising an antistatic agent, saidantistatic agent comprising, in combination, a dispersant and ceriumoxide particles.
 2. The additive concentrate of claim 1, wherein saidfuel comprises a diesel fuel.
 3. The additive concentrate of claim 1,wherein said antistatic agent contributes no more than 0.135 ppm ofsulfur to the additive concentrate.
 4. The additive concentrate of claim1, wherein the cerium oxide particles comprise nanoparticles.
 5. Theadditive concentrate of claim 1, wherein said dispersant comprises asuccinimide dispersant.
 6. The additive concentrate of claim 7, whereinsaid succinimide dispersant is formed from tetraethylene pentamine. 7.Use of the additive concentrate of claim 1 to provide a conductivitymeasure of at least 500 pS/m in a middle distillate fuel after aging for7 days at 21° C.
 8. A middle distillate fuel composition having improvedconductivity, said fuel comprising an antistatic agent, said antistaticagent comprising, in combination, a dispersant and cerium oxideparticles.
 9. The fuel of claim 8, wherein said fuel comprises a dieselfuel.
 10. The fuel of claim 8, wherein said antistatic agent contributesno more than 0.135 ppm of sulfur to the fuel composition.
 11. The fuelof claim 8, wherein said fuel has a conductivity of at least 500 pS/mafter 7 days of aging at 21° C.
 12. The fuel of claim 8, wherein thecerium oxide particles comprise nanoparticles.
 13. The fuel of claim 8,wherein said dispersant comprises a succinimide dispersant.
 14. The fuelof claim 13, wherein said succinimide dispersant is formed fromtetraethylene pentamine.
 15. Use of the fuel of claim 8 in a combustionapparatus.
 16. A method of dispensing a middle distillate fuelcomposition comprising the steps of adding to a middle distillate fuelcomposition an antistatic agent comprising, in combination, a dispersantand cerium oxide particles in an amount sufficient to provide aconductivity benefit to said fuel.
 17. The method of claim 16, furthercomprising the step of dispensing said fuel composition prior to theconductivity of said fuel composition dropping below 50 pS/m.
 18. Themethod of claim 17, wherein said dispensing step comprises dispensingsaid fuel composition into a bulk container.
 19. The method of claim 16,wherein said dispersant and said cerium oxide particles are pre-blendedin an additive concentrate prior to addition to said fuel.
 20. Themethod of claim 16, wherein said fuel comprises a diesel fuel.
 21. Themethod of claim 16, wherein said antistatic agent contributes no morethan 0.135 ppm of sulfur to the fuel composition.
 22. The method ofclaim 16, wherein said cerium oxide particles comprise nanoparticles.23. The method of claim 16, wherein said detergent comprises asuccinimide detergent.
 24. The method of claim 23, wherein saidsuccinimide dispersant is formed from tetraethylene pentamine.
 25. Amethod of reducing a risk of ignition or explosion from staticdischarge, comprising the steps of providing a middle distillate fuelcomposition; adding a combination of a dispersant and cerium oxideparticles to said fuel composition to improve conductivity in said fuelcomposition; thereby reducing the risk of static discharge in said fuelcomposition.
 26. The method of claim 25, further comprising the step ofdispensing the fuel composition.
 27. The method of claim 26, whereinsaid dispensing step comprises dispensing said fuel composition into abulk container.
 28. The method of claim 26, wherein the conductivity insaid fuel composition is at least 50 pS/m at the time and temperature ofdelivery.
 29. The method of claim 25, wherein dispersant and said ceriumoxide particles are pre-blended in an additive concentrate prior tobeing added to said fuel composition.
 30. The method of claim 25,wherein said fuel composition comprises a diesel fuel.
 31. The method ofclaim 25, wherein said middle distillate fuel is substantially free of asulfur-containing conductivity improver.
 32. The method of claim 25,wherein the combination of dispersant and cerium oxide particles add nomore than 0.135 ppm of sulfur to the fuel composition.
 33. The method ofclaim 25, wherein the cerium oxide particles comprise nanoparticles. 34.The method of claim 25, wherein said dispersant comprises a succinimidedispersant.
 35. The method of claim 34, wherein said succinimidedispersant is formed from tetraethylene pentamine.